The Postfix Mail Transfer Agent (MTA) is a widely used MTA, especially on Linux systems.  When testing, or doing maintenance on systems running postfix, you may need to see what messages are in the queue, and/or manipulate the queues.

To see messages in the mail queue, use the following command (this is the same as for sendmail):

mailq

To cause postfix to process the mail queue immediately:

postfix flush

To remove a specific message from the mail queue:

postsuper -d <queue id>

where <queue id> is the identifier of the message (as shown by 'mailq').

Postfix has four mail queues:

• maildrop - locally generated mail.
• incoming - externally arriving mail and processed mail from the maildrop queue.
• active - mail currently being delivered (locally or externally).
• deferred - mail that could not be delivered.  Postfix periodically attempts to redeliver this mail.

To remove all messages from all mail queues, use the special identifier 'ALL':

postsuper -d ALL

To remove all messages from a specific mail queue, add the queue name:

postsuper -d ALL deferred